Metal pretreatment composition containing zirconium, copper, and metal chelating agents and related coatings on metal substrates

ABSTRACT

Disclosed is a zirconium-based metal pretreatment coating composition that includes a metal chelator that chelates copper in the metal pretreatment coating composition and thereby improves adhesion of paints to a metal substrate coated with the pretreatment coating composition and the chelating agent is present in a sufficient amount to ensure that in the deposited pretreatment coating on the metal substrate the average total atomic % of copper to atomic % of zirconium is equal to or less than 1.1. The pretreatment coating composition is useful for treating a variety of metal substrates.

RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.13/796,585, filed Mar. 12, 2013 now U.S. Pat. No. 9,284,460, which is acontinuation of PCT/US2011/063789, filed Dec. 7, 2011, which claimspriority to U.S. Provisional Patent Application No. 61/420,509, filedDec. 7, 2010, which applications are hereby incorporated herein byreference in its entirety.

TECHNICAL FIELD

This invention relates generally to coating compositions, in particular,coating compositions that can be applied to metal substrates to enhancepaint adhesion even after extended coating times. The invention alsorelates to the coatings obtained from the coating composition, methodsof applying these coatings and the coated substrate.

BACKGROUND OF THE INVENTION

A pretreatment coating is often applied to metal substrates, especiallymetal substrates that contain iron such as steel, prior to theapplication of a protective or decorative coating. The pretreatmentcoating minimizes the amount of corrosion to the metal substrate. Inaddition, the pretreatment coating can affect the adhesion ofsubsequently applied decorative coatings such as paints and clear coats.Many of the present pretreatment coating compositions are based on metalphosphates, and/or rely on a chrome-containing rinse. The metalphosphates and chrome rinse solutions produce waste streams that aredetrimental to the environment. As a result, there is theever-increasing cost associated with their disposal. There is aninterest to develop pretreatment coating compositions and methods ofapplying such compositions without producing metal phosphate and chromewaste solutions. It is also preferred, that these pretreatment coatingcompositions be effective in minimizing corrosion and enhancingdecorative coating adhesion on a variety of metal substrates becausemany objects of commercial interest contain more than one type of metalsubstrate. For example, the automobile industry often relies on metalcomponents that contain more than one type of metal substrate. The useof a coating composition effective for more than one metal substratewould provide a more streamlined manufacturing process.

The coating compositions of the present invention are calledpretreatment coatings because they are typically applied after thesubstrate has been cleaned and before the various primer and decorativecoatings have been applied. In the automotive industry, coatings oftencomprise the following layers in order from the substrate out: apretreatment coating for corrosion resistance, an electrodepositedelectrocoat, then a primer layer, a base coat paint, and then a topclear coat. In the present application, all coatings after thepretreatment coating are considered as paints unless otherwise noted.One known pretreatment coating is Bonderite® 958 available from HenkelAdhesive Technologies. The Bonderite® 958 provides a zinc-phosphatebased conversion coating composition that includes zinc, nickel,manganese and phosphate. Currently, Bonderite® 958 is a standardconversion coating used extensively in the automotive industry.

In attempts to move away from conversion coatings that include heavymetals, which as used herein will be understood by those in theconversion coating arts to mean zinc, nickel, cobalt, manganese, andchromium, or that produce phosphate waste streams, a new class ofenvironmentally friendly conversion coating compositions has beencreated. The new class of coatings generally comprises a zirconium-basedconversion coating deposited on a metal substrate by contact with aworking bath containing dissolved zirconium in the coating compositions.These conversion coating compositions, which are based on a zirconiumcoating technology, typically have no phosphates and no nickel ormanganese. Zirconium-based coatings are finding increasing use in theautomotive industry as a pretreatment coating.

Manufacturing plants' metal coating assembly lines are part of anoverall process that is highly coordinated and carefully timed. Metalworkpieces are cut to size, formed, cleaned, coated with a pretreatmentcoating, and then coated with several over layers. Several differenttypes of metal may pass separately through parts of the process to bejoined to each other in one step and then proceed through the remainingprocess steps as an assembly of dissimilar metals. These processes arecarried out on hundreds of pieces per hour and the system requiresprecise movement of a metal workpiece through the process. From time totime, the processing line may be halted, sometimes unexpectedly due to aproblem in one of the processes in the assembly line. When line stoppageoccurs, workpieces are held in the various stages of the line for farlonger than is desirable. When a workpiece is held in a pretreatmentbath too long it is often found that the coated workpiece does notperform up to required standards. For example, the coated workpieces maynot exhibit the desired corrosion resistance or paint adhesioncharacteristics. This can lead to increased scrap rates and potentialrecalls, which can drive up costs of manufacturing. Thus, it isdesirable to provide a pretreatment coating composition that has alonger pot life, meaning that a metal workpiece can be immersed in thebath for a longer period of time without a decrease in the performanceof the coated metal workpiece in corrosion resistance or paint adhesion.

It is also desirable to provide increasing functionality in terms ofenhanced corrosion protection and improved paint adhesion inpretreatment coatings to a wide range of metal substrates. At the sametime, these improvements preferably do not require changes to existingindustrial processes or the equipment used on these processing lines.

Many zirconium-based conversion coating baths contain copper, either asan additive to improve features of the pretreatment coating and/orprocess or as a trace element from water or metal workpieces beingcoated. Regardless of its source, the present inventors have discoveredthat copper from the zirconium-based coating bath that is deposited inthe pretreatment coating at too high an amount relative to other coatingcomponents can negatively affect performance of the coated metalsubstrate. Accordingly, it is desirable to develop zirconium-basedcoating baths that overcome this deficiency.

SUMMARY OF THE INVENTION

In general terms, this invention provides a metal pretreatment coatingthat is zirconium-based and that provides a longer pot life and enhancedpaint adhesion without decreasing the corrosion resistance. Theinvention also relates to the coatings and coated substrate obtainedfrom the coating composition.

In one embodiment, a zirconium-based metal pretreatment coatingcomposition comprising water and dissolved Zr, a source of fluoride, acopper chelating agent, optionally materials comprising one or more ofsilicon, boron and yttrium and optional added dissolved Cu is provided.Desirably, the zirconium-based metal pretreatment coating compositionsaid copper chelating agent is capable of reducing amounts of copperdeposited in a zirconium based coating on a metal substrate by contactwith the zirconium based metal pretreatment coating composition, saidcopper chelating agent present in an amount sufficient to therebyproduce an average total ratio of atomic % of Cu to atomic % of Zr insaid coating deposited on the metal substrate that is equal to or lessthan 1.1.

In one embodiment, a zirconium-based metal pretreatment coatingcomposition is provided, comprising:

A.) 50 to 300 ppm of said dissolved Zr,

B.) 0 to 50 ppm of said added dissolved Cu,

C.) 0 to 100 ppm of SiO2,

D.) 150 to 2000 ppm of total Fluoride,

E.) 10 to 100 ppm of free Fluoride and

F.) at least 10 ppm of said copper chelating agent.

In one embodiment, the added dissolved Cu is present in the coatingcomposition and the copper chelating agent is present in an amount of 25to 1500 ppm.

In one embodiment, the copper chelating agent is selected from moleculeshaving multiple carboxylic and/or phosphonic functional groups.Desirably the copper chelating agent is selected from the groupconsisting of aminosalicylic acid, ascorbic acid, aspartic acid, benzoicacid, citric acid, cyanuric acid, diethylenetriamine-pentamethylenephosphonic acid, dihydroxybenzoic acid, dimethylenetriaminepentaaceticacid, ethylenediaminetetraacetic acid, gluconic acid, glutamic acid,hydroxyacetic acid, hydroxyethylidene diphosphonic acid, hydroxyglutamicacid, iminodisuccinic acid, kojic acid, lactic acid, malonic acid,nitrilotriacetic acid, nitrobenzenesulfonic acid, nitrosalicylic acid,oxalic acid, polyacrylic acid, polyaspartic acid, salicylic acid,tartaric acid, and salts of said acids.

In one embodiment, the zirconium-based metal pretreatment coatingcomposition described above has a copper chelating agent comprisingtartaric acid and/or salts thereof.

Another aspect of the invention is a method for improving paint adhesionto a metal substrate comprising the steps of:

a) optionally cleaning a metal substrate;

b) applying to the metal substrate a zirconium-based metal pretreatmentcoating composition according to any one of the preceding claims,thereby forming a pretreatment coating on the metal substrate;

wherein the copper chelating agent is present in said zirconium-basedmetal pretreatment coating composition in an amount sufficient to resultin an average total ratio of atomic % of Cu to atomic % of Zr in thepretreatment coating deposited on the metal substrate is equal to orless than 1.1; andc) applying a paint to the metal pretreatment coated metal substrate.

Another aspect of the invention is a method for improving paint adhesionto a metal substrate that is subjected to a pretreatment with azirconium-based pretreatment coating composition comprising the stepsof:

a) contacting a metal substrate with a pre-rinse comprising a copperchelating agent, and optionally copper, prior to application of azirconium-based pretreatment coating composition to the metal substrate;

b) applying to the metal substrate a zirconium-based metal pretreatmentcoating composition comprising dissolved Zr, a source of fluoride,optionally materials comprising one or more of silicon, boron andyttrium and optional added dissolved Cu, thereby forming a pretreatmentcoating on the metal substrate;wherein the copper chelating agent is present in the pre-rinse in anamount sufficient to control the amount of copper deposited onto themetal substrate by the zirconium-based pretreatment coating compositionsuch that the average total ratio of atomic % of Cu to atomic % of Zr inthe pretreatment coating deposited on the metal substrate is equal to orless than 1.1.

In one embodiment, the copper chelating agent is present in an amount ofat least 10 ppm and at most 2000 ppm.

Another aspect of the invention is an article of manufacture comprisinga coated metal substrate comprising: a metal substrate; and deposited onsaid metal substrate, a pretreatment coating comprising metal from saidsubstrate, zirconium, oxygen, copper, and optional elements fluorine andcarbon; wherein the pretreatment coating on the metal substrate has anaverage total ratio of atomic % of Cu to atomic % of Zr that is equal toor less than 1.1.

In one embodiment, the article of manufacture is provided whereinaverage total ratio of atomic % of Cu to atomic % of Zr in thepretreatment coating on the metal substrate is about 0.9 to 0.02.

In one embodiment, the article of manufacture is provided wherein atomic% of Cu in said pretreatment coating measured at a series of depths froman outer surface of the pretreatment coating to the metal substrate doesnot exceed 33 atomic % Cu at any of said depths.

In one embodiment, the article of manufacture is provided furthercomprising at least one paint applied to the pretreatment coatingresulting in a painted coated substrate that achieves at least 95% paintremaining when tested according to ASTM 3330M (Revised Oct. 1, 2004).

In one embodiment, the article of manufacture is provided furthercomprising at least one paint applied to the pretreatment coatingresulting in a painted coated substrate that achieves 1.9 mm or lessaverage corrosion creep when tested according to ASTM B117 (Revised Dec.15, 2007) for 500 hours.

In one embodiment, the invention is directed to an aqueous metalpretreatment coating composition comprising: 50 to 300 ppm of dissolvedZr, 0 to 50 ppm of dissolved Cu, 0 to 100 ppm of SiO₂, 150 to 2000 ppmof total Fluoride, 10 to 100 ppm of free Fluoride and a chelating agent.

In one embodiment, the zirconium-based pretreatment coating compositionof the invention provides a pretreatment coating wherein the averagetotal ratio of atomic % of Cu to atomic % of Zr in the pretreatmentcoating on the metal substrate is less than 1.1. In a furtherembodiment, this ratio ranges downward from, in order of increasingpreference 1.10, 1.05, 1.0, 0.95, 0.90, 0.85, 0.80, 0.75, 0.70, 0.65,0.60, 0.55, 0.50 and is not less than, in increasing order of preference0.0001, 0.0005, 0.0010, 0.0050, 0.010, 0.050. In certain embodiments,for example where no added Cu is present in the coating composition, theratio of Cu to Zr in the deposited coating may be zero.

In another embodiment, the invention is directed to a method forimproving paint adhesion to a metal substrate comprising the steps of:providing a metal substrate; applying to the metal substrate an aqueous,zirconium-based metal pretreatment coating composition comprising 50 to300 ppm of dissolved Zr, 0 to 50 ppm of dissolved Cu, 0 to 100 ppm ofSiO₂, 150 to 2000 ppm of total Fluoride, 10 to 100 ppm of free Fluorideand a chelating agent thereby forming a pretreatment coating on themetal substrate wherein a chelating agent is present in an amount suchthat the average total ratio of atomic % of Cu to atomic % of Zr in thepretreatment coating on the metal substrate is equal to or less than1.1; and applying a paint to the metal pretreatment coated metalsubstrate.

The pretreatment coating can be used on a variety of metal substratesincluding cold rolled steel (CRS), hot-rolled steel, stainless steel,steel coated with zinc metal, zinc alloys such as electrogalvanizedsteel (EG), 55% Aluminum-Zinc alloy coated sheet steel, such asGalvalume®, galvanneal (steel sheet with a fully alloyed iron-zinccoating) (HIA), and hot-dipped galvanized steel (HDG), aluminum alloyssuch as AL6111 and aluminum plated steel substrates. One advantage theinvention offers is that components containing more than one type ofmetal substrate can be passivated in a single process because of thebroad range of metal substrates that can be passivated by thepretreatment coating compositions of the invention.

In another embodiment, the invention is directed to a coated substratecomprising a metal substrate having deposited on said metal apretreatment coating comprising metal from the substrate, zirconium,oxygen, copper and optional elements fluorine and carbon; whereinaverage total ratio of atomic % of Cu to atomic % of Zr in thepretreatment coating on the metal substrate is equal to or less than1.1. In one embodiment, the coated substrate further comprises at leastone paint applied to the pretreatment coating wherein the painted coatedsubstrate achieves at least 95% paint remaining when tested according toASTM 3330M (Revised Oct. 1, 2004).

These and other features and advantages of this invention will becomemore apparent to those skilled in the art from the detailed descriptionof a preferred embodiment. Except in the claims and the operatingexamples, or where otherwise expressly indicated, all numericalquantities in this description indicating amounts of material orconditions of reaction and/or use are to be understood as modified bythe word “about” in describing the broadest scope of the invention.Practice within the numerical limits stated is generally preferred.Also, throughout this description, unless expressly stated to thecontrary: percent, “parts of”, and ratio values are by weight; thedescription of a group or class of materials as suitable or preferredfor a given purpose in connection with the invention implies thatmixtures of any two or more of the members of the group or class areequally suitable or preferred; description of constituents in chemicalterms refers to the constituents at the time of addition to anycombination specified in the description or of generation in situ bychemical reactions specified in the description, and does notnecessarily preclude other chemical interactions among the constituentsof a mixture once mixed; specification of materials in ionic formadditionally implies the presence of sufficient counter ions to produceelectrical neutrality for the composition as a whole (any counter ionsthus implicitly specified should preferably be selected from among otherconstituents explicitly specified in ionic form, to the extent possible;otherwise such counter ions may be freely selected, except for avoidingcounter ions that act adversely to the objects of the invention); theterm “paint” includes all like materials that may be designated by morespecialized terms such as primer, lacquer, enamel, varnish, shellac,topcoat, and the like; and the term “mole” and its variations may beapplied to elemental, ionic, and any other chemical species defined bynumber and type of atoms present, as well as to compounds with welldefined molecules.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings that accompany the detailed description are describedbelow.

FIGS. 1A, 1B, 1C, and 1D are scanning electron microscope (SEM) imagesof pretreatment coatings on cold rolled steel;

FIG. 2A is an SEM image of the sample shown in FIG. 1A with severalcircled areas of interest, FIG. 2B is a graph of the chemicalcomposition of the areas circled in FIG. 2A;

FIG. 3A is an SEM image of the sample shown in FIG. 1B with severalcircled areas of interest, FIG. 3B is a graph of the chemicalcomposition of the areas circled in FIG. 3A;

FIG. 4 is a graph of an X-ray photoelectron spectroscopy analysis of thepretreatment coating of FIG. 1A according to the invention; and

FIG. 5 is a graph of an X-ray photoelectron spectroscopy analysis of thepretreatment coating of FIG. 1B.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

The present invention is directed to a metal pretreatment coatingcomposition, and a method for applying the same, as well as to articlesof manufacture comprising coatings according to the invention. Theinvention provides surprising improvements in performance inzirconium-based conversion coating pretreatments such as, by way ofnon-limiting example, zirconium-based conversion coatings deposited on ametal substrate by contact with a working bath containing dissolvedzirconium in the coating compositions. These conversion coatingcompositions are exemplified by aqueous coating baths comprisingdissolved zirconium and free fluoride that form coatings comprisingzirconium and oxygen. The baths are typically aqueous, neutral toacidic, and comprise dissolved zirconium, dissolved copper, either as anadditive or as a trace element from water or metal substrates, and asource of fluoride. Optional components may be present includingmaterials comprising one or more of silicon (e.g. silica, silicates,silanes), boron, yttrium, particular embodiments of which have nophosphates and no zinc, nickel, cobalt, manganese, and chromium.

Many zirconium-based coating baths contain copper, either as an additiveor as a trace element from water or from metal workpieces being coated.Regardless of its source, the present inventors have discovered thatcopper from the zirconium-based coating bath that is deposited in thecoating can negatively affect performance of the coated metal substrate,if present in amounts such that undesirable morphologies in the coatingarise and/or in amounts above desirable levels.

Many zirconium-based pretreatment coating compositions may benefit fromthe invention. The coating baths typically are aqueous, neutral toacidic, and comprise dissolved zirconium, dissolved copper, a source offluoride and counter ions for the dissolved metals, for example sulfatesand/or nitrates. Optional components may be present including materialscomprising one or more of silicon (e.g. silica, silicates, silanes),boron, yttrium. The zirconium-based pretreatment coating compositionsmay contain acid, generally a mineral acid, but optionally organicacids; and/or an alkaline source. The acid and/or alkali may be a sourceof other components in the composition, may be used to control pH orboth. The zirconium-based pretreatment coating compositions according tothe invention may likewise, consist essentially of or consist of thematerials described herein.

The coating composition according to the invention provideszirconium-based coatings having improved paint adhesion and maintainedcorrosion resistance. These and other benefits are achieved by adding toa zirconium-based coating composition, either a bath or the concentrate,a chelating agent, preferably a copper metal chelating agent, to controlthe amount of copper deposited onto the metal substrate by thezirconium-based pretreatment coating composition. This chelating agentcan be added to the zirconium-based pretreatment coating compositioneven where no copper is present in the unused zirconium-basedpretreatment coating composition, as a protective agent to prevent latercopper deposition as the bath ages and copper is incorporated into thebath as a trace element from water, such as from prior cleaning or rinsesteps, and/or from metal workpieces being coated. The inclusion of thechelating agent also extends the pot life of the pretreatment coatingbath because is allows for a wider range of immersion times withoutnegative effects on paint adhesion or corrosion protection.

In one embodiment of the invention, a zirconium-based pretreatmentcoating composition is provided comprising 50 to 300 ppm of dissolvedZr, 0 to 50 ppm of dissolved Cu, 0 to 100 ppm of SiO₂, 150 to 2000 ppmof total Fluoride, 10 to 100 ppm of free Fluoride and a chelating agent.That is, the composition may comprise amounts within the disclosedranges, such as: 50, 60, 70, 80, 90, 100, 120, 130, 140 or 150 ppm to160, 170, 180, 190, 200, 210, 220, 230, 240, 250, 260, 270, 280, 290 or300 ppm of dissolved Zr; 0, 5, 10, 15, or 20 ppm to 25, 30, 35, 40, 45,or 50 ppm of dissolved Cu; 0, 5, 10, 15, 20, 25, 30, 35, 40, 45, or 50ppm to 60, 65, 70, 75, 80, 85, 90, 95 or 100 ppm of SiO₂; 150, 170, 190,200, 225, 250, 275, 300, 325, 350, 375, 400, 425, 450, 475, 500, 525,550, 575, 600, 700, 800, 900, or 1000 ppm to 1150, 1170, 1190, 1200,1225, 1250, 1275, 1300, 1325, 1350, 1375, 1400, 1425, 1450, 1475, 1500,1525, 1550, 1575, 1600, 1700, 1800, 1900, or 2000 ppm of total Fluoride;10, 15, 20, 25, 30, 35, 40, 45, or 50 ppm to 60, 65, 70, 75, 80, 85, 90,95 or 100 ppm of free Fluoride and a chelating agent.

In another embodiment of the invention, a zirconium-based pretreatmentcoating composition is provided comprising 100 to 300 ppm of dissolvedZr, 0 to 50 ppm of dissolved Cu, 0, 25, 50, 75, 100, 200, 300, 400, 500,600, 700, 800, 900, 1000 or 2000 ppm to 2500, 3000, 4000, 4500 or 5000ppm of SO₄, 100 to 1600 ppm of total Fluoride, 10 to 200 ppm of freeFluoride and a chelating agent.

The chelating agent may be any chelating agent capable of reducing theamount of copper deposited in the zirconium based coating. The chelatingagent may be a copper metal chelator. A partial list of exemplarychelating agents, many of which are molecules having multiple carboxylicand/or phosphonic functional groups, that can be used in the presentinvention includes the following: adenine, adenosine, alanine,aminosalicylic acid, ascorbate/ascrobic acid, aspartate/aspartic acid,benzoic acid, citrate/citric acid, cyanuric acid, cysteine, cuprizone,diethanolamine, diethylenetriamine, diethylenetriamine-pentamethylenephosphonic acid, dihydroxybenzoic acid, dimethylenediamine,dimethylenetriamine, dimethylenetriaminepentaacetate (DTPA),dimethylglycine, dimethylglyoxime, ethylenediaminetetraacetate (EDTA),ethyleneglycol, gluconate/gluconic acid, glutamate/glutamic acid,glycerol, glycine, guanine, guanosine, histadine, histamine,hydroxyacetic acid, hydroxyethylidene diphosphonic acid (HEDP),hydroxyglutamic acid, hydroxylamine, iminodisuccinate, kojic acid,lactate/lactic acid, leucine, malonic acid, mannitol, methylglycine,molybdate, nitrilotriacetate, nitrosalicylic acid, ornithine, oxalicacid, polyacrylates, polyaspartates, phenylalanine, salicylic acid,salicylaldoxime, sodium nitrite, sodium nitrobenzenesulfonate,tartrate/tartaric acid, triethanolamine (TEA), triethylenetriamine(TETA), tris(2-aminoethyl)amine (diethylenetriamine), or thioacetamide.

These chelating agents may be utilized according to the followingmethods: they may be incorporated into a pre-rinse applied prior tocontacting the metal substrate with a zirconium-based pretreatmentcoating composition; the chelating agents may be incorporated into azirconium-based pretreatment coating composition as discussed above; thechelating agents may also be applied as a post-rinse applied after themetal substrate has been contacted with a zirconium-based pretreatmentcoating composition.

The chelating agents are used a level sufficient to ensure that in thedeposited pretreatment coating the average total ratio of the atomic %of Cu to the atomic % of Zr in the pretreatment coating on the metalsubstrate is equal to or less than 1.1, preferably from 0.9 to 0.02, andmost preferably from 0.30 to 0.10.

The amount of chelating agent in the coating composition may range from10 ppm to 2000 ppm. The amount required is affected by, for example, theamount of copper present in the coating composition, the temperature ofthe coating bath, the substrate being coated, whether the composition isa concentrate or the working bath and the particular chelating agentbeing used. Chelating agents with multiple coordination sites may beused at lower levels. In one embodiment the chelating agent is presentin an amount ranging from 25-100 ppm in the coating bath. More chelatingagent may be added provided the concentration does not adversely affectbath performance. Desirably, the amount of chelating agent in thepretreatment coating composition is an amount sufficient to achieve adesired Cu:Zr ratio in the deposited coating and preferably thechelating agent amount is at least, in increasing order of preference10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70 or 75 ppm and is atmost, in increasing order of preference, 2000, 1500, 1000, 900, 800,700, 600, 500, 400, 300, 200, 100 ppm.

The average total ratio of atomic % of Cu to atomic % of Zr may rangedownward from, in order of increasing preference 1.10, 1.05, 1.0, 0.95,0.90, 0.85, 0.80, 0.75, 0.70, 0.65, 0.60, 0.55, 0.50. For somezirconium-based pretreatment coating compositions, copper is a desirablepart of the composition and the coating. For some such coatingcompositions, the ratio of copper to zirconium is desirably not lessthan, in increasing order of preference 0.0001, 0.0005, 0.0010, 0.0050,0.010, 0.050.

Zirconium-based pretreatment coatings of the invention may have avariety of components in the coating provided that the amount of copperin the coating is not such that undesirable coating morphology andperformance failures result.

EXAMPLES

In a standard industrial coating process, the immersion bath time for apretreatment coating step is about 120 seconds, but during an assemblyline stoppage this time can be 10 minutes or longer. To simulate a linestoppage and to test various parameters an alternative protocol wasdeveloped by the present inventors. The process used in the experimentsdescribed in the present specification is as shown in TABLE 1 below.

The standard pretreatment process for all of the data, unless otherwisenoted, is as described below in TABLE 1. The Parco® Cleaner 1533R is analkaline cleaner available from Henkel Adhesive Technologies. TheRidosol 1270 is a basic nonionic surfactant and is available from HenkelAdhesive Technologies. The weight ratio of Parco to Ridosol used was8.33 to 1. Aging of the cleaner was simulated by adding the oil Tirroil906 available from Tirreno Industries, to age the cleaner at 4grams/liter. The base pretreatment composition was a zirconium-basedpretreatment. The electrodeposited paint coating used in all of thepaint adhesion tests was BASF Cathoguard 310X available from BASF. Thisis a standard coating used in the automotive industry.

TABLE 1 Time, Temp Stage Treatment Product Application seconds ° C. 1Clean Parco ® Cleaner Spray 70 60 1533R/Ridosol 1270 fresh or aged 2Clean Parco ® Cleaner Immersion 150 60 1533R/Ridosol 1270 fresh or aged3 Rinse City water Spray 60 28 4 Rinse Deionized water Spray 60 25 5Pretreatment zirconium-based Immersion 600 25 pretreatment bath 6Pretreatment zirconium-based Spray 30 25 pretreatment bath 7 RinseDeionized water Spray 60 25 8 Electrodeposited BASF Cathoguard immersion120 32 (230 V) coating 310 X 9 Rinse Deionized water Spray 30 25 10 Bake1200 350° F. or electrodeposited 375° F. paint

Example 1

The zirconium-based pretreatment bath used for Example 1 included 180parts per million (ppm) of zirconium, 30 ppm of copper, 35 ppm of freeand 400 ppm of total fluoride, 42 ppm of SiO₂; the zirconium-basedpretreatment bath pH was set at 4.2. Two different batches ofcommercially available, cold rolled steel (CRS 1 and CRS 2), as istypically used in automobile manufacture, were processed according toTable 1. The zirconium coating weight in milligrams Zr per square meterwas determined for each sample.

In addition for each sample, the paint adhesion of the BASF Cathoguard310 X was determined using the following protocol. A sample area wascross hatched down to the level of the substrate with a razor using aline spacing of 1 millimeter and 6 lines for each direction. Then a 75millimeter long strip of adhesive tape 20 millimeters wide was appliedto the cross hatched area. The tape adhesively bonds to steel accordingto ASTM 3330M (Revised Oct. 1, 2004) with a 180 degree peel strengthvalue of 430 N/m. After 5 to 10 seconds of adhesion, the tail end of thetape was grasped and pulled upward with a rapid jerking motionperpendicular to the paint. The percent paint remaining attached to thesubstrate (indicative of paint adhesion) was determined as a percentageof the area covered by the tape. The results of Example 1 are reportedbelow in TABLE 2.

TABLE 2 Zr coating Bake Sample CRS weight temperature % paint No. sampleCleaner mg/m² ° F. remaining 1 CRS 1 1533/1270 143 350 100 fresh 2 CRS 11533/1270 203 350 100 aged 3 CRS 1 1533/1270 143 375  99-100 fresh 4 CRS1 1533/1270 203 375 100 aged 5 CRS 2 1533/1270 165 350 95-98 fresh 6 CRS2 1533/1270 182 350  99-100 aged 7 CRS 2 1533/1270 165 375 60-70 fresh 8CRS 2 1533/1270 182 375  80 aged

The results demonstrated a bake temperature effect on theelectrodeposited coating adhesion. When the bake temperature of theelectrodeposited paint was raised from 350° F. to 375° F., there was areduction in paint adhesion, especially on the CRS 2 substrate. Theresults for CRS 2 were also quite different than for CRS 1. Furtherexamination of samples from each CRS revealed striking differences inthe deposited pretreatment coating composition. FIGS. 1A and 1B are at amagnification of 10,000× and 1C and 1D are a magnification of 30,000×.

Sample 3:

FIGS. 1A and 1C are scanning electron microscope (SEM) photographs ofCRS 1 coated with a pretreatment coating composition according toExample 1, using fresh 1533/1270, a Zr coating weight of 143 mg/m² and abake temperature of 375° F. as described above (Sample 3).

Sample 7:

FIGS. 1B and 1D are SEM photographs of CRS 2 coated with a pretreatmentcoating according to Example 1, using fresh 1533/1270, a Zr coatingweight of 165 mg/m² and a bake temperature of 375° F. as described above(Sample 7). Sample 7, the CRS 2 sample exhibited poor paint adhesion.

The photographs show that the deposited pretreatment coating of Sample 3in FIGS. 1A and 1C was composed of much smaller substructures than thatfound in the pretreatment coating surface of Sample 7 in FIGS. 1B and1D. The surface in FIGS. 1B and 1D had larger and more clumped lookingsubstructures.

Sample 3:

FIGS. 2A and 2B are a further analysis of the Sample 3 surface shown inFIGS. 1A and 1C. FIG. 2A shows an SEM photograph of the pretreatmentcoating at a magnification of 15,000× and also shows three circleslabeled 1, 2, and 3. Each of these areas was subjected to Auger EmissionSpectroscopy (AES) to identify the elements and their levels found ineach area of analysis. The results were evaluated by looking at thedeviation from the baseline for each area, to make comparison possiblethe baselines were offset as can be seen. The units on the y-axis inFIG. 2B are (counts/second)×10⁵, that is, the y-axis amounts wereincreased by a factor of 100,000. The results show differences in thelevels of copper between the three areas. The iron, zirconium and carbonlevels were all very similar in the three areas. The largestsubstructure, area 1, had the highest level of copper. By way ofcontrast area 2, a very small substructure, had very little copper init. Finally, area 3, which was taken between two larger substructures,showed a copper level that was between areas 1 and 2. The actual levelsof copper were as follows: area 1 had a copper level of 27 atomicpercent; area 2 had a copper level of 5 atomic percent; and area 3 had acopper level of 6 atomic percent. This represents a pretreatment coating(Sample 3) that led to good paint adhesion as shown in TABLE 2.

Sample 7:

FIGS. 3A and 3B show a further analysis of the surface shown in FIGS. 1Band 1D (Sample 7). FIG. 3A shows an SEM photograph of the pretreatmentcoating at a magnification of 15,000× and also shows two circles labeled4 and 5. Each of these areas was subjected to AES to identify theelements and their levels found in each spot of analysis. The resultswere evaluated by looking at the deviation from the baseline for eacharea, to make comparison possible the baselines were offset as can beseen. The units on the y-axis of FIG. 3B are (counts/second)×10⁴, thatis, the y-axis amounts were increased by a factor of 10,000, therefore 1unit in FIG. 3B is equal to 10 units in FIG. 2B. Area 4 is of a largesubstructure and the AES analysis showed that it had a very high levelof copper, much higher than that found in the large substructure shownin FIGS. 2A and 2B, area 1. In addition, area 5, a small substructureshowed lower levels of copper than area 4, but much higher than evenarea 1 of FIGS. 2A and 2B considering the differences in the units. Theactual values for Sample 7, FIG. 3B, were as follows: area 4 had acopper level of 31 atomic percent and area 5 had a copper level of 25atomic percent, much higher on average than those of Sample 3, which hadgood paint adhesion. These results show that excess copper in thedeposited pretreatment coating caused poor paint adhesion and led toformation of larger substructures which was also not beneficial forpaint adhesion. Pretreatment coatings with good paint adhesion tended tohave smaller and fewer substructures and less deposited copper.

FIGS. 4 (Sample 3) and 5 (Sample 7) are graphical representations of theresults from X-ray photoelectron spectroscopy (XPS) depth analysis ofthe two sample pretreatment coatings described in FIGS. 2 (Sample 3) and3 (Sample 7), respectively. In this analysis an argon beam was used topenetrate the coating and as it moved through the coating the atomicpercentages of the coating components were determined at a series ofdepths from the outer surface of the coating. The spot size for analysiswas approximately 2×2 millimeters. Once the atomic percentage of iron(Fe) exceeded 50% the beam had reached the underlying CRS substrate.Turning to FIG. 4 (Sample 3), the box outline represents thepretreatment coating, it can be seen that the coating was approximately145 nanometers thick while the coating of FIG. 5 (Sample 7) wasapproximately 220 nanometers thick. The Figures further confirmed thathigher copper levels in the coating correlated to poor paint adhesion:FIG. 5, showing a graph of Sample 7, the sample exhibiting poor paintadhesion, showed that the copper levels in the deposited pretreatmentcoating were much higher than in Sample 3, the pretreatment coatingexhibiting good paint adhesion, whose graph is shown in FIG. 4. Both theatomic percentage and the area under the curve for the copper were muchgreater in FIG. 5 (Sample 7) compared to FIG. 4 (Sample 3). The peakatomic % Cu in FIG. 4 (Sample 3) was 33 atomic %. The peak atomic % Cuin FIG. 5 (Sample 7) at any depth was 42.73 atomic %.

In further testing it has been determined that enhanced paint adhesionis seen when the pretreatment coating composition has sufficientchelating agent to ensure that the deposited pretreatment coating on themetal substrate has a average total ratio of the atomic % of copper tothe atomic % of zirconium equal to or less than 1.1, more preferably theratio is from 0.9 to 0.02, and most preferably from 0.3 to 0.1. Thisratio is determined from the average overall atomic percentages of theZr and Cu in the coating not from the ratio at a single depth. As can beseen in the data from FIGS. 4 (Sample 3) and 5 (Sample 7), as one movedthrough the coating composition down to the metal substrate the atomicpercentage of the coating components varied by depth until one reachedthe metal substrate, so it is the total overall average atomic % ratiothat must be determined. By way of contrast, the overall average totalratio of atomic % of Cu to atomic % of Zr seen in the depositedpretreatment coating composition shown in FIGS. 1B, 1D, 3, and 5 (Sample7) was 2.73. The results led the inventors to develop the hypothesisthat controlling the amount of deposited copper in the pretreatmentcoating, in the presence of copper in the pretreatment bath, couldimprove paint adhesion and also extend the pot life of zirconium-basedpretreatment coatings baths, which was tested in Example 2 below.

Example 2

In Example 2, the control pretreatment coating composition was azirconium-based coating bath, wherein the Zr level was 180 ppm, Cu was30 ppm, total Fluoride was 400 ppm and free Fluoride was 35 ppm, thelevel of SiO₂ was 42 ppm. The test pretreatment coating composition wasthe same as the control and further comprising a chelating agent,tartrate introduced as tartaric acid at 50 ppm. The pH of thepretreatment coating compositions was adjusted to 4.0. The substrate wasCRS that had been pre-cleaned with fresh Parco® 1533 and rinsed asdescribed in TABLE 1 above. The immersion time in the control and thetest zirconium-based coating baths was either 4 minutes or 10 minutes,simulating a shorter and a longer line stoppage. A portion of each setof samples were then further coated with BASF Cathoguard 310X asdescribed above and baked at 375° F. The baked samples were then testedfor paint adhesion as described above. In addition, the coating weightsof Zr in mg/m² were determined for the samples. Finally the averageatomic percentage of Zr and Cu in the pretreatment coatings wasdetermined for each sample. The results are present below in TABLE 3.

TABLE 3 Zr Paint Pretreatment Immersion coating Average Average Ratioadhesion coating time wt. atomic atomic of % Example bath minutes mg/m²% Cu % Zr Cu/Zr remaining Comp. zirconium- 4 166 3.8 3.3 1.15 90 Ex. 2-1based coating bath Comp. zirconium- 10 340 9.1 7.6 1.20 50 Ex. 2-2 basedcoating bath Ex. 2-3 zirconium- 4 115 2.5 2.6 0.96 100 based coatingbath, plus 50 ppm tartrate Ex. 2-4 zirconium- 10 182 4.0 5.2 0.77 100based coating bath, plus 50 ppm tartrate

The results of Table 3 showed that an increased immersion time led to anincrease in Zr coating weight, amount of Zr deposited, and the amount ofCu deposited. Inclusion of the tartrate at 50 ppm reduced the Zr coatingweight, the amount of Zr deposited, and the amount of copper depositedin the pretreatment coating. More significantly, the presence oftartrate enhanced the pot life of the zirconium-based coating bath. Thisis seen by the fact that with tartrate present in the coating bath, thepaint adhesion remains at 100% even after a 10 minute immersion, whereasin the absence of tartrate, the paint adhesion was significantly reducedto 90% or 50% of the applied paint coating. This tends to show that toomuch copper, relative to zirconium, deposited during the zirconium-basedpretreatment coating bath can reduce paint adhesion and shorten pot lifeof the coating bath and that chelating agents, particularly copper metalchelators can improve paint adhesion and pot life.

Example 3

In a next series of experiments, the effect of inclusion of the metalchelator tartrate on corrosion performance was tested. Again thesubstrate was CRS. The CRS was treated as described below in TABLE 4.The 2 minute treatment in the zirconium-based coating immersion bath isa standard time used in the industry.

As a separate control samples of the CRS were also treated with thepretreatment coating Bonderite® 958 and sealer Parcolene® 91, bothavailable from Henkel Adhesive Technologies per the manufacturer'sdirections. As a final control CRS samples were simply cleaned withParco® Cleaner 1533R/Ridosol 1270 fresh and rinsed with no pretreatmentcoating. Then all the samples were coated with the BASF Cathoguard 310X,rinsed and baked.

TABLE 4 Time, Temperature Stage Treatment Product Application seconds °C. 1 Clean Parco ® Cleaner Spray 70 60 1533R/Ridosol 1270 fresh 2 CleanParco ® Cleaner Immersion 150 60 1533R/Ridosol 1270 fresh 3 Rinse Citywater Spray 60 28 4 Rinse Deionized water Spray 60 25 5 Pretreatmentzirconium-based Immersion 120 or 25 coating bath with or 600 without 50ppm tartrate 6 Pretreatment zirconium-based Spray 30 25 coating bathwith or without 50 ppm tartrate 7 Rinse Deionized water Spray 60 25 8Electrodeposited BASF Cathoguard immersion 120 32 (230 V) coating 310 X9 Rinse Deionized water Spray 30 25 10 Bake 1200 375° F.electrodeposited

Samples were then scribed to the CRS substrate and subjected to one oftwo corrosion performance tests. The first test was according to ASTMB117 (Revised Dec. 15, 2007) for 500 hours. In a second test, a 31 cycletest, the sample panels were subjected to 31 cycles of a 24 hour testingprotocol using a salt misting spray. The salt misting spray comprised0.9% by weight sodium chloride, 0.1% by weight calcium chloride, and0.075% by weight sodium bicarbonate at pH 6 to 9. The first 8 hours thepanels were kept at 25° C. and 45% Relative Humidity (RH) and misted 4times during the 8 hours at time 0, 1.5 hours, 3 hours and 4.5 hours.The panels were then put at 49° C. and 100% RH for the next 8 hours witha ramp up from 25° C. to 49° C. and 100% RH over the first hour. Thefinal 8 hours were at 60° C. and less than 30% RH with a ramp to the newconditions of 3 hours. The cycle was carried out for a total of 31times. The panels were then evaluated for average creep and maximumcreep in millimeters from the scribe line. The results for the ASTM B117test are presented in TABLE 5. The results for the 31 cycle corrosiontest are presented in TABLE 6.

TABLE 5 ASTM B117 Maximum Corrosion Average Corrosion Pretreatmentcreep, millimeters creep, millimeters zirconium-based coating bath, 93.9 2 minutes zirconium-based coating bath, 3.5 2.5 10 minuteszirconium-based coating bath, 6 3 2 minutes, 50 ppm tartratezirconium-based coating bath, 3 1.9 10 minutes, 50 ppm tartrateBonderite ® 958/ 2 1.3 Parcolene ® 91

TABLE 6 31 Cycle Corrosion Test Maximum Corrosion Average CorrosionPretreatment coating creep, millimeters creep, millimeters Clean only 1110.4 zirconium-based coating bath, 3.8 3.1 2 minutes zirconium-basedcoating bath, 5.3 4.3 10 minutes zirconium-based coating bath, 4.2 3.6 2minutes, 50 ppm tartrate zirconium-based coating bath, 4.5 3.8 10minutes, 50 ppm tartrate Bonderite ® 958/ 2.2 2.2 Parcolene ® 91

The results indicate that inclusion of the tartrate did not have anegative effect on the ability of the zirconium-based pretreatmentcoating to provide corrosion resistance to the CRS. Under the ASTM 8117500 hour test the results of using the tartrate were at least as good asthe standard zirconium-based coating bath and were slightly better forextended dwell time of the CRS in the bath evidencing the improved potlife from the chelator. The longer immersion times did not reduce thecorrosion protection and may even increase it. In the 31 cycle test thebenefit of using a pretreatment coating was shown, in the clean onlysample there was much more corrosion than in any of the pretreatmentcoating examples. The presence or absence of the tartrate did not seemto affect the corrosion protection ability of the pretreatment coating.These results are important because if the presence of a chelatingagent, such as the tartrate, was detrimental to the corrosion protectionthen one would have to balance that negative effect against thebeneficial effect on paint adhesion.

Example 4

In a next series of experiments the effects of another chelating agent,triethanolamine (TEA), were tested. The substrate was CRS and thepretreatment coating and BASF Cathoguard were applied as described belowin TABLE 7. Again the zirconium-based coating bath included 180 ppm ofZr, 30 ppm of Cu, 35 ppm of free and 400 ppm total Fluoride and 42 ppmof SiO₂. Samples were then tested for Zr coating weight in mg/m², paintadhesion, and corrosion protection under ASTM B117 for 500 hours. As acontrol samples were also prepared with a pretreatment coating ofBonderite® 958 and Parcolene® 91 as described in Example 3. The resultsare presented below in TABLE 8. Only a single concentration of TEA wastested, the same level as used for tartrate of 50 ppm.

TABLE 7 Time, Temperature Stage Treatment Product Application seconds °C. 1 Clean Parco ® Cleaner Spray 70 60 1533R/Ridosol 1270 fresh 2 CleanParco ® Cleaner Immersion 150 60 1533R/Ridosol 1270 fresh 3 Rinse Citywater Spray 60 28 4 Rinse Deionized water Spray 60 25 5 Pretreatmentzirconium-based Immersion 240 or 600 25 coatings bath with or without 50ppm TEA 6 Pretreatment zirconium-based Spray 30 25 coating bath with orwithout 50 ppm TEA 7 Rinse Deionized water Spray 60 25 8Electrodeposited BASF Cathoguard immersion 120 32 (230 V) coating 310 X9 Rinse Deionized water Spray 30 25 10 Bake 1200 375° F.electrodeposited paint

TABLE 8 Zr coating Paint Maximum Average Pretreatment weight adhesion %creep creep (ND = not determined) mg/m² remaining millimetersmillimeters zirconium-based coating bath, 4 122 60 9 3.9 minuteimmersion zirconium-based coating bath, 202 50 3.5 2.5 10 minuteimmersion zirconium-based coating bath, 115 98 11.8 8.8 plus 50 ppm TEA,4 minute immersion zirconium-based coating bath, 231 90 4.8 3.3 plus 50ppm TEA, 10 minute immersion Bonderite ® 958/Parcolene ® 91 0 ND 2.0 1.3

The results again demonstrate the benefit of including a chelatingagent, in particular a copper metal chelator, in the pretreatmentcoating on the paint adhesion. In the presence of 50 ppm of TEA thepaint adhesion was significantly enhanced, even with a long immersion of10 minutes. The results show that at this level of TEA there was anegative effect on corrosion protection. Clearly, the optimum level ofcopper metal chelator is dependent on the identity of the chelator.There was also no reduction of Zr coating weight with TEA at 50 ppm.

The foregoing invention has been described in accordance with therelevant legal standards, thus the description is exemplary rather thanlimiting in nature. Variations and modifications to the disclosedembodiment may become apparent to those skilled in the art and do comewithin the scope of the invention. Accordingly, the scope of legalprotection afforded this invention can only be determined by studyingthe following claims.

We claim:
 1. An article of manufacture comprising a coated metalsubstrate which has been coated according to a method comprising stepsof: a) contacting a metal substrate with a pre-rinse comprising a copperchelating agent, and optionally copper, prior to application of azirconium-based pretreatment coating composition to the metal substrate;b) applying to the metal substrate a zirconium-based metal pretreatmentcoating composition comprising dissolved Zr, a source of fluoride,optionally materials comprising one or more of silicon, boron andyttrium and optional added dissolved Cu, thereby forming a pretreatmentcoating on the metal substrate; wherein the copper chelating agent ispresent in the pre-rinse in an amount sufficient to control the amountof copper deposited onto the metal substrate by the zirconium-basedpretreatment coating composition such that an average total ratio ofatomic % of Cu to atomic % of Zr in the pretreatment coating depositedon the metal substrate is in a range of 0.0001 and 1.1.
 2. The articleof manufacture according to claim 1, wherein the average total ratio ofatomic % of Cu to atomic % of Zr in the pretreatment coating on themetal substrate is about 0.9 to 0.02.
 3. The article of manufactureaccording to claim 1, wherein the average total ratio of atomic % of Cuto atomic % of Zr in the pretreatment coating on the metal substrate isabout 0.3 to 0.1.
 4. The article of manufacture according to claim 1,wherein atomic % of Cu in said pretreatment coating measured at a seriesof depths from an outer surface of the pretreatment coating to the metalsubstrate does not exceed 33 atomic % Cu at any of said depths.
 5. Thearticle of manufacture according to claim 1, wherein the metal substratecomprises cold rolled steel.
 6. The article of manufacture according toclaim 5, further comprising at least one paint applied to thepretreatment coating resulting in a painted coated substrate thatachieves at least 95% paint remaining when tested according to ASTM3330M (Revised Oct. 1, 2004).
 7. The article of manufacture according toclaim 5, further comprising at least one paint applied to thepretreatment coating resulting in a painted coated substrate thatachieves 1.9 mm or less average corrosion creep when tested according toASTM B117 (Revised Dec. 15, 2007) for 500 hours.
 8. An article ofmanufacture comprising a coated metal substrate comprising: a metalsubstrate; and deposited on said metal substrate, a pretreatment coatingcomprising metal from said substrate, zirconium, oxygen, copper, andoptional elements fluorine and carbon; wherein the pretreatment coatingon the metal substrate has an average total ratio of atomic % of Cu toatomic % of Zr that is equal to or less than 1.1.
 9. The article ofmanufacture according to claim 8, wherein the average total ratio ofatomic % of Cu to atomic % of Zr in the pretreatment coating depositedon the metal substrate that is in a range of 0.0001 and 1.1.
 10. Thearticle of manufacture according to claim 8, wherein the average totalratio of atomic % of Cu to atomic % of Zr in the pretreatment coating onthe metal substrate is about 0.9 to 0.02.
 11. The article of manufactureaccording to claim 8, wherein the average total ratio of atomic % of Cuto atomic % of Zr in the pretreatment coating on the metal substrate isabout 0.3 to 0.1.
 12. The article of manufacture according to claim 8,wherein the elements fluorine and carbon are present in the pretreatmentcoating and wherein atomic % of Cu in said pretreatment coating measuredat a series of depths from an outer surface of the pretreatment coatingto the metal substrate does not exceed 33 atomic % Cu at any of saiddepths.
 13. The article of manufacture according to claim 8, wherein themetal substrate comprises cold rolled steel.
 14. The article ofmanufacture according to claim 13, further comprising at least one paintapplied to the pretreatment coating resulting in a painted coatedsubstrate that achieves at least 95% paint remaining when testedaccording to ASTM 3330M (Revised Oct. 1, 2004).
 15. The article ofmanufacture according to claim 13, further comprising at least one paintapplied to the pretreatment coating resulting in a painted coatedsubstrate that achieves 1.9 mm or less average corrosion creep whentested according to ASTM B117 (Revised Dec. 15, 2007) for 500 hours.